Cyclic ethers, unsaturated

Hodgson and coworkers extended this concept to epoxides of unsaturated cyclic ethers 128 [5] and amines 130 [46, 47] (Scheme 5.28). It is interesting that the use of trimethylsilylmethyllithium as the organolithium in this case resulted in substituted allylsilanes 129 and 131 (R = CH2SiMe3) presumably the epoxide ring protons of 128 and 130 are more acidic than those of a simple terminal epoxide (see Scheme 5.26). 

Fragmentation Losses from the molecular ions are 1, 29, and 30 Daltons with the loss of 29 (CHO) being characteristic of cyclic ethers. This loss also appears in the mass spectra of unsaturated cyclic ethers, such as furans and benzofurans. The fragmentation of saturated cyclic ethers generally shows a M — 1 ion. 

A series of functionalized alkenes has been subjected to selective epoxidation reactions. Oxidation of perfluorinated vinyl polyethers by bubbling oxygen through the liquid that contains a catalytic amount of a Lewis acid, e.g. antimony(V) fluoride, results in the formation of acid fluorides together with a smaller amount of C = C bond cleavage.76 Perfluorinated pentaaIkyI-2.3-dihydrofuran 38, an example of an unsaturated cyclic ether that is quite stable owing to perfluoroalkylation. is epoxidized by hypochlorite to the product 39 at 45 C.62... 

Exercise 13-21 Devise a synthesis of 3-hexyn-1,6-diol from two-carbon compounds using the unsaturated cyclic ether, >, as a protecting reagent for hydroxyl... 

An excellent reagent to form acetals is the unsaturated cyclic ether, 16. This ether adds alcohols in the presence of an acid catalyst to give the acetal 17 ... 

Purine itself methylates only at the 9-position1S0 with dimethyl sulfate or methanolic diazomethane, no 7-isomer being obtained. With mono-,25 di-,80,87 and trichloropurines,54 alkaline dimethyl sulfate or methyl iodide gives mixtures of the 7- and 9-isomers. Even with alkylation by 3-bromocyclohexene,131 where steric factors may apply, both isomers are obtained with 6-ehloropurine. Acid conditions also favor attack in the five-membered ring, where the 9-isomer is preferentially formed. When unsaturated cyclic ethers, such as... 

Propenyl Ethers and Unsaturated Cyclic Ethers Propenyl ethers (CH3—CH=CH—OR R = ethyl, isobutyl, etc. cis- and trans-isomers) and 3,4-dihydrofuran are linear and cyclic a,/3-unsaturated ethers, that can be regarded as / -substituted vinyl ether derivatives. For these monomers a few controlled/living cationic polymerizations have been reported. The HI/I2 system is generally effective for both linear and cyclic monomers [181,182,183], whereas a recent study by Nuyken indicates that the IBVE-HI adduct coupled with nBu4NC104 is suited for 3,4-dihydrofuran (see Section V.A.4) [184]. A variety of mono- and bifunctional propenyl ethers can readily be prepared by the ruthenium complex-catalyzed isomerization of corresponding allyl ethers [185]. 

Both processes were complicated, however, by the occurrence of elimination-addition-elimination sequences to give unsaturated cyclic ethers (21) and (23). The general mechanism outlined in Fig. 49 is suggested. 

Problem 17.15 The unsaturated cyclic ether furan can readily be made from substances isolated from oat hulls and corncobs one of its important uses involves its conversion into (a) tetrahydrojiiran, and (b) 1,4-dichlorobutanc. Using your knowledge of alkene chemistry and ether chemistry, show ho N these conversions can be carried out. 

Allylically unsaturated cyclic ethers of the same general type... 

Tetrahydrooxepin-2-yl acetate is a seven-membered unsaturated cyclic ether, which undergoes ROMP to give an 80% cis polymer (Hocker 1984). 

More recently, iodonium salts have been widely used as photoinitiators in the polymerization studies of various monomeric precursors, such as copolymerization of butyl vinyl ether and methyl methacrylate by combination of radical and radical promoted cationic mechanisms [22], thermal and photopolymerization of divinyl ethers [23], photopolymerization of vinyl ether networks using an iodonium initiator [24,25], dual photo- and thermally-initiated cationic polymerization of epoxy monomers [26], preparation and properties of elastomers based on a cycloaliphatic diepoxide and poly(tetrahydrofuran) [27], photoinduced crosslinking of divinyl ethers [28], cationic photopolymerization of l,2-epoxy-6-(9-carbazolyl)-4-oxahexane [29], preparation of interpenetrating polymer network hydrogels based on 2-hydroxyethyl methacrylate and N-vinyl-2-pyrrolidone [30], photopolymerization of unsaturated cyclic ethers [31] and many other works. 

From acetylenic compounds, central or terminal, dichlorocyclobutenones are formed.247 Diacetylenic compounds provide the monoadducts in the two cases tested. a-Unsaturated cyclic ethers (dihydrofuran and -pyran) xmdergo a clean reaction.248 With 1,4-dioxene, a convenient access to semisquaric acid is obtained, even if the yield of the first step is modest.249... 

Both alkyl and aryl vinyl ethers and a variety of unsaturated cyclic ethers will undergo free-radical copolymerization with MA, under mild conditions, to give equimolar copolymers. DuPlessis and coworkers have shown that dialkyl maleates and alkyl vinyl ethers will also undergo equimolar copolymerization. This occurs even though all of the monomers are very sluggish to free-radical homopolymerization. In some cases, spontaneous or thermal copolymerization can even occur between vinyl ethers and MA, such as 1,2-dimethoxyethylene, " p-dioxene, and conjugated dihydro-anisole. It is also known that vinyl ethers will polymerize in the presence of amide-MA mixtures, with the amide-MA CTC playing the role of initiator. ... 

Several different types of unsaturated cyclic ethers, such as p-dioxene, 2,3-dihydropyran, furan, 2-methylfuran, 2,3-dihydrofuran, 2,2-dimethyl-l,3-dioxole, 2-methylene-oxetane, and benzofuran have been copolymerized with MA. Only the 2-methylene-oxetane fails to copolymerize in a 1 1 fashion with MA. 

Shimo, X, Iwakiri, T. and Somekawa, K., Peri-selective photocycloadditions of methyl 2-pyrone-5-carboxylate with unsaturated cyclic ethers, J. Heterocyclic Chem., 29, 199, 1992. 

Keywords A f/-Markovnikov addition Enol esters Hydration Nucleophilic addition Ruthenium catalysis Unsaturated cyclic ethers Vinyl carbamates... 

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